1. Field of the Invention
This disclosure relates to peer-to-peer networks and the filtering of information available for storage on peer-to-peer networks.
2. Related Art
Peer-to-peer networks are an autonomous network of computers that communicate with one another. Users of peer-to-peer networks make their files available for sharing by advertising available files, that is, broadcasting the availability of the files to peers and by allowing downloads of available files by peers on the network. Peer-to-peer networks may contain a broad variety of content, the distribution of which may infringe the copyright of the owner of the content. Content may include music, photographs, books, magazines, movies, televisions shows, and other works which may be protected by copyright laws. Example peer-to-peer networks include FastTrack, eDonkey, Gnutella and BitTorrent. As peer-to-peer networks proliferate, copyright holders seek the means to remove infringing material availability on peer-to-peer networks.
For centralized networks an index of available content is held in a central database, and all searches for available content on the network are conducted through the central database. As such, the central database may identify and remove infringing content. However, for decentralized peer-to-peer networks, there is no central database of available content. Peer-to-peer networks provide a distributed, ad hoc indexing function. The indexing function is distributed in that typically no one node on the network contains a copy of the entire list of content that is available on the network. Instead, hundreds, thousands or even millions of nodes contain small indexes, each containing a subset of the total available content. The index functionality is ad hoc in the sense that indexing nodes may go offline or come online at any time, and that any particular node may or may not be capable of providing indexing functionality.
The unruly group of distributed ad hoc indexing nodes that provide the content on peer-to-peer networks has been viewed by some as uncontrollable, in that there has been no successfully widely deployed technique to prevent the distribution of copyright infringing content. Content owners and technology companies have focused their efforts on filtering content from peer-to-peer networks using two techniques. These two techniques are referred to herein as “point of search/download solutions” and “point of sharing solutions.”
A. Point of Search/Download Solutions
Point of search/download solutions attempt to filter out infringing content from being displayed in search results at the peer-to-peer network user's computer. An example point of search/download solution may perform the following actions:                1. User A initiates a peer-to-peer search for a file having a specified keyword by using a peer-to-peer application on user A's computer to contact other nodes on the peer-to-peer network requesting search a list of available files which match the keyword.        2. If any matching files are found, search results containing information about those files (which may be or include“metadata”) is returned to User A's peer-to-peer application.        3. Before displaying the search results, User A's peer-to-peer application may evaluate whether the search results include links to infringing content. For example, User A's peer-to-peer application may contain a filter list of keywords representing infringing content, such as names of artists whose works are owned by a particular copyright holder. When the search results contain one or more keywords included in a filter list, the peer-to-peer application may block the matching search result from being displayed. Or, for example, User A's peer-to-peer application may contact a server to learn whether the search results contain any infringing content.        
A point of search/download solution removes search results and/or the ability to download infringing content by filtering out (that is, removing) from those results infringing entries so that infringing content is not displayed to the user in response to a search by that user.
Point of search/download solutions have numerous and obvious problems, including the following: a) A filter list of all infringing content must be distributed to the computer of every user on the network. b) Every node on the network may be required to check with a filter server to evaluate the search results before displaying the search results to the user. c) To achieve a) and b) requires that the filter server have enormous bandwidth and processing capacities which causes the point of search/download solution to be very expensive to run. d) There are privacy issues that may arise if users' search queries and/or search results are passed to a filter server. The owners of the filter server and/or the government authorities may inspect the search results and, by correlating those search requests and/or results with users' IP addresses, may monitor the behavior of users in a way that falls outside of their mandate of preventing the distribution of selected copyright infringing works. For example, a government authority in a repressive country may use such means to charge a particular user on the network with searching for homosexual content, or for searching for information on freedom charters, etc. e) Finally, any user who obtains a hacked version of the peer-to-peer application—i.e. a version of the peer-to-peer application where the filtering function has been removed or circumvented—may be able to obtain unfiltered search results. There is therefore a direct and obvious motive for hackers to attempt to create such a derivative unfiltered product and for users to download such a product en masse. In other words, shortly after the product has been hacked, as it inevitably would be, any user who wishes to obtain access to infringing content, or who wishes to avoid the privacy concerns outlined above, will replace their existing filtered version of the peer-to-peer application software with the hacked version. As a result of these problems, a point of search/download solution has no or limited success as a tool for preventing distribution of infringing content on peer-to-peer networks.
B. Point of Sharing Solutions
Point of sharing solutions provide another approach. Instead of trying to filter incoming search results on a user's personal computer, a point of sharing solution tries to prevent a user from sharing infringing files. That is, the point of sharing solutions block infringing files from being made available on the network by a given user, so that infringing files will not appear as a search result to users. Stated another way, point of sharing solutions prohibit peer-to-peer applications from advertising infringing content. However, to achieve this, as with point of search/download solutions, each computer must keep a large filter list or check with a server before advertising a particular file.
Point of sharing solutions suffer similar problems as point of search/download solutions, including: a) Requiring a filter server to handle a large amount of network traffic to evaluate advertised files before they are shared. b) High operating costs caused by the network traffic of a). b) Privacy issues like those described above, at least as great as those outlined above, and possibly greater, because the central authority now potentially has knowledge of each file shared by every user on the network. c) The incentive to create a hacked version of the peer-to-peer application is a little less than for the point of search/download solution, because there is little to be gained by using a hacked version. d) However, if even, say, 10% of users make use of a hacked version of the client peer-to-peer application and are able to share infringing content, then the content may become readily available on the network. As such, point of sharing solutions have no or limited success as a tool for preventing distribution of infringing content on a peer-to-peer network.